1. Field of the Invention
The present invention relates to a head-up display on a vehicle, and in particular, to a technique of controlling the brightness of a displayed image.
2. Description of the Related Art
Conventionally, a system on a vehicle for detecting a pedestrian or the like ahead of the vehicle is known, wherein two cameras are mounted on the vehicle, and the distance between the target object and the vehicle is determined based on the difference between the images taken by the two cameras, that is, by using parallax. Japanese Unexamined Patent Application, First Publication, No. Hei 9-226490 discloses a detector for crossing objects, which is an example of the above-explained system.
In such conventional systems, typically, the driver is warned of the existence of a target object with which the vehicle may collide by only an alarm mounted on the vehicle. Therefore, if the driver specifies or identifies the wrong object as the target object, the message of the alarm will not be correctly communicated to the driver.
In consideration of the above circumstances, an objective of the present invention is to provide a head-up display on a vehicle for calling the attention of the driver or passenger to a dangerous object and for making the driver or passenger reliably recognize a communicated alarm.
Therefore, the present invention provides a head-up display on a vehicle (e.g., vehicle 1 in the embodiment explained below), comprising:
an image display device (e.g., HUD control section 31 and HUD body 32 in the embodiment explained below) for displaying an image taken by a camera (e.g., IR camera 11R or 11L in the embodiment explained below) on the vehicle;
a detecting device (e.g., night vision unit 33 and peripheral vehicle recognizing unit 34 in the embodiment explained below) for detecting a target object in the vicinity of the vehicle;
a switching device (e.g., display start/stop operating section 12 in the embodiment explained below) for manually switching between a display state in which the image is displayed by the image display device and a warm-up state in which the image is invisible; and
a warning device (e.g., night vision unit 33 (which also functions as the above detecting device) in the embodiment explained below) for outputting a control signal based on a result detected by the detecting device, thereby making the image display device display the image, and
wherein a brightness employed by the image display device for displaying the image according to the control signal is higher than a brightness employed by the image display device for displaying the image according to a manual operation of the switching device.
According to the above structure, typically, the head-up display is activated and switched on when the vehicle is started by switching on the ignition, and the head-up display enters the warm-up state. After that, if a target object which seems like it will collide with the vehicle is detected based on an image taken by the camera or by a peripheral vehicle recognizing unit or the like, or if a manual operation of the switching device is performed by the driver who wishes to confirm an image, then the image taken by the camera is displayed in an image display area on a front window, or the like. Here, the brightness employed by the image display device for displaying the image according to the control signal is higher than the brightness employed by the image display device for displaying the image according to the manual operation of the switching device. Therefore, the driver can be reliably informed of the relevant alarm.
That is, when the driver (or passenger) manually commands the image display by using the switching device, it is determined that the driver wishes to confirm a dangerous situation or the like. On the other hand, when the image is displayed according to the control signal output from the warning device, the driver does not expect the output of a control signal (that is, an alarm). However, in this case, the image is displayed with a higher brightness, thereby reliably attracting the driver""s attention, and preventing the driver from erroneously recognizing the target object.
Preferably, when the image display device displays the image according to the control signal from the warning device, the image display device reduces the brightness after a predetermined time (e.g., t2xe2x88x92t1 or t3xe2x88x92t1 in the embodiment explained below) from the starting of the display. Accordingly, when a control signal is again output, the brightness of the displayed image can be increased again, thereby making the driver or passenger reliably recognize the alarm relating to this control signal.
Typically, in the warm-up state, the image is displayed with a brightness by which the image is invisible to the driver or passenger of the vehicle; and
when a predetermined time (e.g., t4xe2x88x92t1 in the embodiment explained below) has elapsed after the image display device starts to display the image, the display state is shifted to the warm-up state.
Accordingly, during ordinary driving, the driver""s vision is not obstructed by the image displayed on the front window, for example, and when the control signal is output, the brightness of the image can be quickly increased, thereby reducing the time lag from the command to the display start, and making the driver or passenger reliably recognize the relevant alarm.
Preferably, the image display device has a light source (e.g., light source 21 in the embodiment explained below) for changing the brightness of the displayed image according to an applied voltage supplied to the light source; and
when the image display device is commanded to display the image by a manual operation of the switching device or the control signal output from the warning device, the image display device supplies the maximum applied voltage (e.g., Vf in the embodiment explained below) to be applied to the light source for a predetermined time (e.g., tfxe2x88x92t1 in the embodiment explained below).
Accordingly, when the starting of the image display (i.e., display state) is commanded, even when the applied voltage corresponding to a target brightness is lower than the maximum applied voltage to be supplied to the light source, the maximum applied voltage is temporarily supplied, and the applied voltage corresponding to the target brightness can be employed when the brightness reaches the target brightness. Therefore, the time necessary for the light source to reach the target brightness can be reduced, thereby improving the response of the image display operation, and making the driver or passenger quickly recognize the relevant alarm.
It is possible that the detecting device outputs an alarm signal when detecting a target object in the vicinity of the vehicle; and
the image display device displays a predetermined still image according to the alarm signal output from the detecting device, and
wherein the brightness employed by the image display device for displaying the still image according to the alarm signal is higher than the brightness employed by the image display device for displaying the image according to a manual operation of the switching device.
Preferably, when the image display device displays the still image according to the alarm signal from the detecting device, the image display device reduces the brightness after a predetermined time from the starting of the display.
It is also possible that when both the control signal from the warning device and the alarm signal from the detecting device are output, the image display device displays the image taken by the camera and the still image which are overlapped.